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FFMPEG Notes

  • Render only a part of the video: -ss 10:20 -to 10:30 -ss and -to arguments must be entered first
ffmpeg -i input.mkv -vf zscale=t=linear:npl=100,format=gbrpf32le,zscale=p=bt709,tonemap=tonemap=hable:desat=0,zscale=t=bt709:m=bt709:r=tv,format=yuv420p,scale=1920:-1,subtitles=subs.srt -c:a libfdk_aac -b:a 128k -ac 2  -c:v h264_nvenc -pixel_format yuv420p -cq:v 25 -b:v 0 -movflags +faststart output.mp4
  • -vf: Video filter, list, separated by ,
  • Use H.264 encoding with nvenc: -c:v h264_nvenc
  • H.264 quality (lower the better quality): -cq:v 25 -b:v 0 (don't change -b:v 0)
  • Convert audio to AAC format: -c:a libfdk_aac -b:a 128k
  • Convert to stereo sound: -ac 2
  • Optimise for playing on the web: -movflags +faststart
ffmpeg -i input.mkv -map 0:3 subs.srt
  • Extract subs from the video to a srt file.
  • Select stream 0:3 to convert: -map 0:3 (get stream name from ffmpeg -i <file>)
ffmpeg -y -hwaccel_device 0 -hwaccel cuda -init_hw_device opencl=gpu:0.0 -filter_hw_device gpu -vsync 0 -i input.mkv -vf scale=1920:-1,subtitles=hp3.srt,format=yuv420p,hwupload,nlmeans_opencl=p=5:r=11,hwdownload,format=yuv420p -pixel_format yuv420p -c:a libfdk_aac -ac 2 -c:v h264_nvenc -cq:v 22 -b:v 0 -movflags +faststart ./hp3-v3.mp4
  • A bunch of flags that I don't understand to enable the use of GPU in filters: -hwaccel_device 0 -hwaccel cuda -init_hw_device opencl=gpu:0.0 -filter_hw_device gpu
  • Video filters
    • Denoise: nlmeans_opencl=p=5:r=11
    • Upload/download frames to GPU for opencl filters: hwupload hwdownload
      • Put a format filter right after hwdownload to change downloaded format

Notes on use subtitle filter with -ss

Trim the srt file before use it in the filter:

ffmpeg -ss 0:10 -i input.srt output.srt

Denoise

ffmpeg -i input.mp4 -af "highpass=f=200, lowpass=f=2000" out.mp4

Crop Video

ffmpeg -i input.mp4 -filter:v "crop=80:60:200:100" -c:a copy out.mp4
  • out_w is the width of the output rectangle
  • out_h is the height of the output rectangle
  • x and y specify the top left corner of the output rectangle

Get First Frame

ffmpeg -i input.mp4 -vframes 1 -f image2 ./first_frame.jpg
Last update: November 21, 2021
Created: April 14, 2021